The present invention relates to an improvement in anodes of non-aqueous electrolyte secondary batteries.
Non-aqueous electrolyte secondary batteries including lithium or a lithium compound for the anode are expected to have a high voltage and high energy density, and therefore, they are extensively studied.
Known cathode active materials for the non-aqueous electrolyte secondary batteries are oxides and chalcogens of transition metals, such as LiMn.sub.2 O.sub.4, LiCoO.sub.2, LiNiO.sub.2, V.sub.2 O.sub.5, Cr.sub.2 O.sub.5, MnO.sub.2, TiS.sub.2, MoS.sub.2 and the like. These compounds have a layered or tunneled crystal structure to allow lithium ions to freely intercalate and deintercalate. The use of metallic lithium for the anode active material has intensively been examined. Such use, however, has a drawback; lithium dendrite occurring on the surface of metallic lithium in the course of charging results in lowering the charge-discharge efficiency and may come into contact with the cathode to cause an inner short circuit.
In order to solve this problem, the potentials for application of lithium alloys, such as lithium-aluminum, which can depress the growth of lithium dendrite and absorb and desorb lithium, for the anode have been studied. However, when lithium alloys are used for the anode, repeated charge and discharge causes pulverization of the alloys, posing a problem of poor cycle life characteristics.
There are proposals for solving this problem by inhibiting pulverization of the alloys by including additional elements in the lithium-aluminum alloy (for example, Japanese Laid-Open Patent Publication Sho 62-119856 and Hei 4-109562), although the improvement is not sufficient. Lithium ion batteries recently developed have anodes composed of carbon material that reversibly intercalates and deintercalates lithium and has excellent cycle characteristics and safety though having a smaller capacity than those of the anode active materials mentioned above.
With a view to enhancing the capacity, a number of studies have proposed application of oxides for the anode; for example, crystalline oxides, such as SnO and SnO.sub.2 (Japanese Laid-Open Patent Publication Hei 7-122274 and Hei 7-235293) and amorphous oxides, such as SnSiO.sub.3, SnSi.sub.1-x P.sub.x O.sub.3 (Japanese Laid-Open Patent Publication Hei 7-288123). These oxides, however, do not sufficiently improve the characteristics.